One study, led by Dr. Joshua Thorpe, included nearly 76,000 older Veterans who had a diagnosis of dementia and were enrolled in both VA care and Medicare Part D, which covers drugs for Medicare beneficiaries.

About 80 percent of the Veterans used only VA care, while the others received prescriptions in both systems.

The study found problems with potentially unsafe prescribing in both groups. Overall, more than 4 in 10 Veterans were exposed to potentially unsafe medication. But those who got prescriptions in the two systems–rather than only in VA–were at double the risk.

The study used a composite score that tracked exposure to three problematic classes of drugs: any high-risk drug not recommended for seniors; those drugs known to have cognitive side effects; and antipsychotics, which carry especially high risk for those with dementia.

The researchers say the results agree with those from past studies that found worse outcomes for Veterans who juggle their health care between VA and Medicare.

Lack of integration between the systems

One factor could simply be a lack of integration between the two systems. In the case of dementia, these patients might be especially hard-pressed to keep track of prescriptions from multiple providers.

One solution, say the researchers, would be an electronic medical record system that allows for easy sharing between VA and non-VA providers. Pilot work along these lines is underway.

A greater role for pharmacists could also help. VA pharmacists could serve as "medication coordination managers" across both systems, say the researchers.

The dementia study appeared online Dec. 6, 2016, in the Annals of Internal Medicine.

The other study, led by Dr. Walid Gellad, focused on Veterans who were being treated for opioid addiction with buprenorphine. The drug is itself a type of opioid, but it can help patients wean themselves from more dangerous drugs like heroin.

However, when buprenorphine is used along with certain other drugs, the risk increases. These include other opioids, and benzodiazepines–tranquilizers such as Valium or Xanax, which have high potential for abuse.

The study, published online Dec. 7, 2016, in the journal Substance Abuse, included 1,790 dually enrolled Veterans with buprenorphine prescriptions, either from VA or Medicare Part D, or from both systems.

Among the VA buprenorphine recipients, 26 percent had an overlapping opioid prescription and 1 percent an overlapping benzodiazepine prescription from Part D.

Among Part D buprenorphine recipients, 19 percent had an overlapping opioid prescription and 16 percent an overlapping benzodiazepine prescription from VA.

In up to a third of the cases of cross-system opioid overlap, the prescriptions overlapped for three months or longer.

'Medical data sharing has to become a priority'

Gellad, lead author on the opioid study and a coauthor on the dementia research, published an editorial earlier this year in the Journal of General Internal Medicine in which he examined dual health system use, particularly in the context of the Veterans Choice Act. The 2014 law widened the circumstances under which Veterans enrolled in VA care could get care from non-VA doctors.

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Gellad noted that "prior work has documented convincing evidence that dual use of Medicare and VA services comes with inherent risks related to care fragmentation and duplication of services." These included higher risks of hospitalization for certain conditions, and higher cost and worse outcomes in cancer.

He concluded that "if dual healthcare system use is to become the norm within VA, then improving medical data sharing has to become a priority."